Linear microwave source for plasma surface treatment

ABSTRACT

The invention relates to a linear microwave source for the treatment of surfaces comprising: 
     a tight enclosure (1), 
     means (B 1 , B 2  ; A 1 , A 2 ) for producing a magnetic field in the enclosure and for generating a plasma layer (P), 
     coupling means between the microwave emission means and the enclosure (1), 
     at least one target (2), 
     pumping means (3), 
     gas injection means (9) for checking the ion species of the plasma layer (P). 
     Particular application to plasma surface treatment.

TECHNICAL FIELD

The present invention relates to a linear microwave source for plasmasurface treatment.

PRIOR ART

In electron cyclotron resonance sources, the ions are obtained byionizing, within a sealed enclosure of the superhigh frequency cavitytype and having an axis of symmetry, a gaseous medium constituted by oneor more gases or metal vapours. This ionization results from aninteraction between the gaseous medium and a plasma of electrons highlyaccelerated by electron cyclotron resonance. This resonance is obtainedby means of the combined action of a high frequency electromagneticfield injected at a first end of the enclosure and a magnetic fieldhaving an axial symmetry prevailing in said same enclosure.

French patent application 86 10066 of Jul. 10, 1986 describes such acyclotron resonance ion source having:

a sealed enclosure with a longitudinal axis of symmetry, a first and asecond ends oriented in accordance with said axis, said enclosurecontaining a gas for forming by cyclotron resonance a plasma confinedwithin said enclosure;

a device for injecting at the first end of the enclosure a highfrequency electromagnetic field;

a magnetic structure arranged around the enclosure and having an axis ofsymmetry coinciding with that of the enclosure, producing axial andradial, local magnetic fields, defining at least one equimagnetic layeron which the electron cyclotron resonance condition is satisfied, saidmagnetic structure comprising:

a first and a second coils positioned on either side and equidistantlywith respect to a median plane, perpendicular to the longitudinal axisof the enclosure and passing through the centre of the cavity, said twocoils being traversed by currents having opposing flow directions and

means for concentrating magnetic force lines surrounding the enclosurein the median plane and locally reinforcing the radial magnetic fieldsin said plane;

a system for extracting from the enclosure the ions formed and locatedat the second end of the enclosure.

Several other prior art documents relate to plasma sources.

Patent application WO-A-92/21136 (Material Research Co.) describes anapparatus for the treatment of electronic "wafers" having the followingfeatures:

the device revolves about an axis,

the microwave power is applied by a cylindrical cavity excited by anarray of distributed loops,

the magnetic field is produced by distributed magnets, said field havinga symmetry of revolution and being highly inhomogeneous,

for compensating said inhomogeneity of the field and the plasma themagnets rotate.

Such a source with a revolution geometry cannot be transposed to alinear geometry.

Japanese abstract (Vol. 10, no. 158, 6.6.1986; JP-A-61-013 634)describes a device whose magnetic configuration is of revolution.

The configuration of the cusp is that used in fusion machines. The cuspconfiguration is used for eliminating in the radial direction highenergy particles, which can cause defects in the deposition. In saidconfiguration the cusp is not an active element.

Patent application EP-A-252,845 (CEA) describes an electron cyclotronresonance ion source. This source has an enclosure containing a gas forforming a confined plasma, a device for injecting at one end of theenclosure a hf electromagnetic field, two coils arranged around theenclosure and supplied in opposition, located on either side of a medianplane perpendicular to the longitudinal axis of the enclosure, aring-shaped, soft iron shield surrounding the enclosure and located inthe median plane, the coils and the shield defining at least oneequimagnetic layer on which the electron cyclotron resonance conditionis satisfied, as well as a system for extracting the ions formed andlocated at the second end of the enclosure.

Several prior art documents deal with couplers:

The article entitled "Lower-hybrid plasma heating via a newlaunchers--The multijunction grill" by Gormezano et al (Nuclear Fusion,vol. 25, No. 4, 1985, Vienna, Austria, pp. 419-423).

The article entitled: "Coupling of slow waves near the lower hybridfrequency in JET" by Litaudon et al (Nuclear Fusion, vol. 30, no. 3,1990, Vienna, Austria, pp. 471-484).

The article entitled: "A 4 waveguide multijunction antenna for L. H. H.in PETULA" by N'Guyen et al (Proceedings of the 13th symposium on fusiontechnology, vol. 1, 24-28 Sep. 1984, Varese Italy, pp. 663-668).

The article entitled: "The 15 Mw microwave generator and launcher of thelower hybrid current drive experiment on JET" by Pain et al (Proceedingsof the IEEE 13th symposium on fusion engineering, 2-6 Oct. 1989, vol. 2,Knoxville, USA, pp. 1083-1088).

The article entitled: "First operation of multijunction launcher onJT-60" by Ikeda et al (Proceedings of the 8th topical conference onradiofrequency power in plasmas, 1-3 May 1989, no. 190, Irvin, Canada,pp. 138-141).

The article entitled: "Technological developments in lower hybridcoupling structures in FT and FTU" by Ferro et al (Proceedings of the11th symposium on fusion engineering, 18-22 Nov. 1985, vol. 2, Austin,Tex., pp. 1210-1213).

U.S. Pat. No. 4,110,595 (Brambilla et al).

In all these documents the aim is to slow down a wave. This is broughtabout by associating guides by the large side and imposing a regularphase shift Δψ between each guide. The coupling of the wave is obtainedby placing said array of guides perpendicular to the magnetic field.

In all these documents there is a superimposing of independent VHFmodules in order to make available the maximum power in the surface of afusion machine (JET, JT 60, TORE SUPRA). These guides are associated ineach module by the large side and are perpendicular to the magneticfield.

However, the field of the present invention is the production of verylong plasma layers (e.g. exceeding 1 meter) and coupling a microwavepower with said plasma layer with a view to the treatment of largesurfaces.

To this end, the invention aims at solving a certain number of problemsexisting in the prior art devices, in order to reduce costs, facilitateuse and obtain better results, in particular:

producing a planar magnetic configuration, whose plane of symmetry isidentical to that of the plasma layer,

production over the entire width of the plasma layer of a constantmagnetic field making it possible to obtain the resonance conditionbetween the frequency of the wave and the electron cyclotron frequencyover the entire width of said layer,

possibility of varying the magnetic configuration in order to adapt thecharacteristics of the plasma to the chosen surface treatment type,

use of the coupler ensuring a uniform distribution of the microwavepower over the plasma layer and a wave plane perpendicular to themagnetic field,

desired modularity of the source,

obtaining homogeneous target wear,

obtaining a good adaptation of the different elements used: coupler,plasma, target, to the desired deposit,

obtaining a good operation despite the large dimensions of theinstallations,

obtaining a controlled deposit independently of the formation of theplasma layer.

DESCRIPTION OF THE INVENTION

The invention proposes a linear microwave source functioning without anelectrode, in a wide pressure range and generating a plasma layer whosedimensions are adapted to the treatment of large surfaces.

This linear microwave source for the plasma treatment of surfaces ischaracterized by the implementation of:

a tight enclosure,

an array of coils and/or magnets making it possible to generate planarmagnetic configurations, whose plane of symmetry corresponds to that ofthe plasma layer,

coupling means between the microwave power sources and the plasma layerin the enclosure,

at least one target, constituted by at least one element to bedeposited, which is electrically insulated from the enclosure and raisedto a bias voltage relative to the plasma layer,

pumping means for producing the vacuum in the enclosure,

gas injection means for checking the ion species of the plasma layer,

a magnetic field having a plane of symmetry coinciding with that of theplasma layer and that of the enclosure,

a constant magnetic field in the direction of the plasma layer width,which makes it possible to obtain the resonance condition 2πf₀ =eB_(RES) /m over the entire plasma layer width.

Apart from the advantage of functioning without an electrode in a widepressure range and generating a plasma layer whose dimensions areadaptable to the application adopted, the microwave source according tothe invention can, as a function of the arrangement of the coils andpermanent magnets, function with several magnetic configuration types:

a planar configuration of the "magnetic mirror" type making it possibleto produce a very dense plasma layer and an ion flux, whosecharacteristics are particularly appropriate to a process for thecoating of large parts by target sputtering;

a planar configuration of the "magnetic cusp" type appropriate for theproduction of a metallic plasma layer for depositing thin metallic oralloy films on substrates;

a planar configuration of the "hybrid" type favouring the production ofmulticharged ions for the requirements of ion implantation on largesurfaces.

The coupling of the microwave power with the plasma layer is broughtabout by waveguides associated or joined along their large or smallsides, permitting a uniform distribution of said power over the entireplasma layer and the excitation of a wave or vibration planeperpendicular to the magnetic field.

In a preferred embodiment the coupler is constituted by identical VHFmodules, each module grouping several guides joined along the large sideand supplied from a main guide by means of a planar multijunction E orseveral secondary guides joined along the small side and supplied from amain guide by means of a taper E and H and a mode converter. At afrequency of 2.45 GHz, this solution is particularly simple andeconomic, because each VHF module can be supplied by a magnetron-type,medium power, microwave emitter or transmitter.

This method of associating or joining guides makes it possible to adaptthe surface of the plasma layer generated in the source to thedimensions of the parts to be treated and in particular to large parts.

Advantageously the coupling means are at least partly made from amaterial which is that of the target, which makes it possible to obtainhigh quality metal deposits, contamination by impurities then beingreduced. The source assembly is grounded or earthed. The enclosure has aparallelepipedic shape. The frequency of the electromagnetic fieldproduced within the enclosure is in the range 1 to 10 GHz.

In a first variant, the means for producing a magnetic field comprisecoils, the length of the coils exceeding the length of the vacuumenclosure, so as to eliminate the edge effects linked with the return ofthe current.

In a second variant, the means for producing a magnetic field comprisepermanent magnet blocks located on either side of the vacuum enclosure,the permanent magnet blocks being extended beyond the vacuum enclosurein order to prevent edge effects.

In a first embodiment, the source according to the invention has amirror-type magnetic configuration comprising two identical coil arraystraversed by equal currents flowing in the same direction, or twoidentical magnet blocks hollowed out in their central portion andlocated on either side of the vacuum enclosure, the magnetic fieldhaving two maxima B_(MAX) and one minimum B_(MIN) between said maxima,the condition B_(MAX) >B_(RES) >B_(MIN) being satisfied over the entirewidth of the plasma layer, B_(RES) being the value of the magnetic fieldfor which the cyclotron angular frequency of the electron is equal tothe angular frequency of the electromagnetic wave used for producing theplasma.

Compared with the magnetron method currently used for this coatingprocess, this type of source offers numerous advantages. The ionizationof the gas, the sputtering of the target, the recombination of thetarget atoms on the part to be treated are very strongly decoupled,which gives a very considerable flexibility in the performance of theprocess. The ion density n_(i) in the source is fixed by the gas flowrate .left brkt-top.o and the microwave power P_(VHF) and the velocityof the ions V₂, which bombard the target by the voltage of said targetV_(c). The deposition rate on the part, which is proportional to the ionflux on the target, can thus be controlled in independent manner by thethree parameters .left brkt-top.o, P_(VHF) and V_(c). This e.g. makes itpossible to optimize the coefficient of sputtering of ions on the targetby the target V_(c) and optimize the density in the source n_(i) withthe parameters .left brkt-top.o and P_(VHF). Moreover, in said sourcesthe neutral atoms emitted by the target recombine on the part to betreated in a region which does not face the plasma. Thus, for a constantion flux supplied by the source, the pressure in the work frame or rackcan be lowered by using a differential pumping. The wave ionizationmechanism used enables the ion flux given to the target to operate withlower pressures in the source, which limits the density of occludedgases in the deposit. The material balance is improved because theentire surface of the target is bombarded by the plasma layer. Inaddition, the target can be charged without dismantling the source orpassing in front of the ion beam for carrying out a continuous process.

In this embodiment the source can be used for supplying a beam of ionsor electrons.

For this embodiment the target is replaced by extraction electrodes. Thefirst electrode facing the plasma layer is placed at the potential ofthe vacuum enclosure and the second electrode is positively polarized inorder to extract the electrons or negatively polarized to extract theions.

In a second embodiment the source according to the invention has amagnetic cusp configuration in which the currents passing through thecoils or magnetization vector in the magnet blocks have opposite signs,the coils and the magnets being dimensioned so as to satisfy thecondition B_(xMAX), B_(yMAX) >B_(RES) over the entire plasma layerwidth.

Apart from the possibility of producing deposits on large substrates, byits very operating principle this type of source has, compared with thegenerally used sources, a number of important advantages. The waveionization mechanism eliminates pollution of the deposit linked with theuse of an emissive cathode and permits an operation of the source at lowpressure, which limits the density of the occluded gases. The magneticcusp configuration offers a new possibility of checking the nature andquality of the deposit. The latter point is important with respect tothe flexibility of use of such sources.

In a third embodiment, the source according to the invention has ahybrid magnetic configuration generated by the superimposing of amirror-type magnetic field produced by two coils surrounding the vacuumenclosure and a transverse magnetic field produced by two permanentmagnet blocks located on either side of the vacuum enclosure.

The advantage of this configuration is that it generates a planarsurface in the plasma, where the resonance condition |B|=B_(RES) issatisfied at all points of said surface. This property is essential forthe formation of multicharged ions in the plasma.

The field of application of this type of source covers all the fields ofapplication of conventional ion sources, namely ion implantation,deposition with ion assistance, etc. The unique advantage of this typeof source is that it permits the performance of such processes on anindustrial level as a result of the dimensions and performancecharacteristics of the generated ion beam.

In each of these embodiments, the absence of an emissive cathode makesit possible to enable the sources to operate with reactive gases underpermanent conditions with a remarkable reliability and service life.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a to 1c illustrate a magnetic mirror source according to theinvention in a configuration using coils.

FIGS. 2a to 2c illustrate the magnetic mirror source according to theinvention in a configuration using permanent magnets.

FIG. 2d illustrates a variant of the source according to FIGS. 2a to 2c.

FIGS. 3a and 3b illustrate a variant of the source of FIGS. 1a and 1c.

FIGS. 4 to 6 illustrate different characteristics of the sourceaccording to the invention.

FIGS. 7 to 7c illustrate a cusp source according to the invention in aconfiguration using coils.

FIGS. 8 to 8c illustrate a cusp source according to the invention in aconfiguration using permanent magnets.

FIG. 9 illustrates a microwave source having a hybrid configuration.

DETAILED DESCRIPTION OF EMBODIMENTS

According to the invention specific properties of a plasma layer createdin a cyclotron resonance ion source and the generation of a plasma, suchas the density, ionization rate and dimensions are based on thesimultaneous implementation of a linear magnetic configuration, theionization of the gas by a wave of frequency f_(o), the use of theresonant properties of said wave at the electron cyclotron resonancef_(o) =f_(ce) =eB/m (e: electron charge; B magnetic field module, melectron mass) and the possibilities thereof of propagating at highdensity in the form of the lower hybrid mode and the uniform excitationof said wave throughout the plasma layer by means of a couplerconstituted by identical, juxtaposed associated waveguides.

The magnetic configuration of such a source is produced by coils orpermanent magnets. As a function of the direction and intensity of thecurrent in the coils or the magnetization in the permanent magnets, itis possible to obtain three magnetic configuration classes:

a mirror-type magnetic configuration,

a cusp-type magnetic configuration,

a hybrid magnetic configuration.

These sources, as a function of the magnetic configuration used,generate a plasma, whose characteristics are specifically adapted to therequirements:

of coating by sputtering (first configuration),

the deposition of thin metal layers (second configuration),

ion assistance and implantation (third configuration).

In the following description, the frequency f_(o) of the wave is notdefined, because the source according to the invention operates in awide frequency range between a few hundred megahertz (MHz) and a fewdozen gigahertz (GHz). Within said range 1 to 10 GHz offers numerousadvantages. Thus, power emitters exist, the performance characteristicsof the permanent magnets are compatible with the resonance condition ofthe wave f_(o) =eB/2πm and the characteristics of the plasma are adaptedto the envisaged applications. In particular at the industrial frequencyof 2.45 GHz, for which there are numerous small and medium poweremitters of the magnetron type and high power emitters of the klystrontype, there is a great flexibility in the distribution of said powerover the guides of the coupler and a good compromise between the priceof these sources and the performance characteristics of the plasma.

The basic circuit of a magnetic mirror-type source used for coating apart by sputtering a target 2 by ion bombardment is illustrated in FIGS.1a to 1c and 2a to 2c. In FIGS. 1b and 1c the magnetic mirror isproduced by coils B₁ and B₂ and in FIGS. 2b and 2c by permanent magnetsA₁ and A₂. FIGS. 1a and 2a show the variation of the magnetic field Bxin the plane of symmetry of the source (Y=0). FIGS. 1b and 2b correspondto a section of the source in the form of a planar cross-section (xOyplane) and FIGS. 1c and 2c to a section according to a longitudinalcross-section (yOz plane). This source is constituted by a vacuumenclosure 1, an array of coils B₁, B₂ or permanent magnets A₁, A₂creating the magnetic configuration and a coupler distributing withinthe enclosure the VHF power generated by the microwave emitter oremitters.

The vacuum enclosure 1 is parallelepipedic. The height of itscross-section (xOy plane; FIGS. 1b and 2b) is chosen so as to permit thepassage of the waveguides of the coupler. The width is determined by thedimensions of the coils and the magnets. The length of its longitudinalcross-section (yOz plane) is only fixed by the size of the parts to betreated. The enclosure 1 is connected to the work frame or rack 4 bymeans of a clamp 8. As a function of the type of use, the vacuum in theenclosure is produced by an autonomous pumping unit or by the work framepumping unit 3.

In FIGS. 1b and 1c, as well as 2b and 2c the coupler permitting thetransfer of the microwave power P_(VHF) to the plasma layer isconstituted by guides associated or joined along the large side. In thiscase the guides are grouped by identical modules. Each VHF module issupplied by a main guide 13 via an adapter, a main guide/overdimensionedguide transition 12, a planar division E 11, a tight window 10 andseveral secondary guides 15. The association of these VHF modules makesit possible to adapt the size of the generated plasma layer to the sizeof the parts to be treated.

The coupler emits a plasma layer P in the direction of the target 2polarized at voltage V_(c). A flow 6 of neutral charges from the targetis then emitted in the direction of the part 5 to be treated on which isproduced a deposit 7.

The enclosure 1 is equipped with at least one gas injection system 9 forchecking ion species of the plasma.

In the configuration shown in FIGS. 1b and 1c the magnetic field isproduced by two coil arrays B₁ and B₂ traversed by currents I₁ and I₂ inthe same direction. These coils surround the vacuum enclosure 1. Theirlength exceeds that of the enclosure in order to eliminate the edgeeffects linked with the return of the current. Under these conditionsthe vector potential A generated by these coils has a single componentin the volume of the enclosure A_(z) (x,y) and the two components of themagnetic field Bx and By are fixed by the relations ##EQU1##

For two identical coil arrays B₁ and B₂ traversed by identical currentsI₁ and I₂ in the same direction, the magnetic field B in the plane ofsymmetry (y=0) has the conventional shape of so-called magnetic mirrorfields used in revolution geometry fusion machines. This field has twomaxima B_(MAX) at the centre of the coils and one minimum B_(MIN)between the coils. The shape of the coils, the distance separating themand the currents flowing through them are chosen so as to satisfy thecondition B_(MAX) >B_(RES) >B_(MIN) over the entire plasma layer width.B_(RES) is the magnetic field value for which the cyclotron angularfrequency of the electron ce=eB_(RES) /m is equal to the angularfrequency of the electromagnetic wave used for producing said plasmaω_(o) =2πf₀ =e B_(RES) /m.

The use of coils for generating the magnetic configuration has theadvantage of a high source operating flexibility. Within the conditionB_(MAX) >B_(RES) >B_(MIN) the characteristics of the magnetic mirror caneasily be modified by acting on the currents I₁ and I₂, the distancebetween the coils and the number of windings supplied in each coil.

This in particular makes it possible to adjust the position of thecyclotron resonance (B_(RES)) in the mirror and with respect to thecoupler in order to optimize the characteristics of the plasma (density,electron temperature, working pressure), modify the mirror ratio inorder to act on the leakage flux of the plasma on the extraction side orcheck the impact surface of the plasma on the target. FIGS. 3a and 3billustrate a variant of the source according to FIGS. 1a to 1c with anasymmetrical magnetic mirror. In this case the target is moved closer tothe coupler and positioned between the coils B₁ and B₂. According to theadopted sputtering deposition process, this source operating variant isof interest, because it makes it possible to very easily vary, by actingon the current I₂, the density of the ion flux bombarding the target. Italso makes it possible to adjust the magnetic field gradient 2B/2_(x) tothe frequency of the wave used.

A linear configuration with a magnetic mirror like that shown in FIGS.1b and 1c can be obtained on the basis of samarium-cobalt oriron-neodymium-boron, parallelepipedic permanent magnets. These magnetsare assembled to form two identical blocks A₁ and A₂ arranged on eitherside of the vacuum enclosure, as shown in FIG. 2b. In the longitudinaldirection (Oz), said blocks are extended beyond the vacuum enclosure toavoid edge effects, as shown in FIG. 2c. These two magnet blocks A₁ andA₂ are hollowed out in the central portion. The characteristics of themagnetic mirror (B_(MAX), B_(MIN), mirror length and ratio) are fixed bythe widths and heights of the two external blocks of the mirror l₁ andh₁ and the central block l₂ and h₂, as shown in FIG. 4.

Within the condition B_(MAX) >B_(RES) >B_(MIN), the characteristics ofthe mirror can be adjusted by acting on the distance between the magnetand the enclosure e, on the gaps between the magnet blocks, or bysupplying metal parts, which are arranged in known manner for thepurpose of modifying the magnetic field lines.

The great advantage of using magnets is to produce a magneticconfiguration without an electric power source. As the microwave poweris transmitted to the plasma by waveguides, the source assembly isearthed, which facilitates the integration of such a source type into anindustrial process.

The power supplied in this way by the microwave emitter or emittersP_(VHF) is introduced into the enclosure 1 by means of waveguideslocated at the end of the magnetic mirror.

At low power, the electric E(ω_(o)) and magnetic H(ω_(o)) fields excitedin the guides are essentially perpendicular to the magnetic fielddirection, which permits the propagation of the wave in the form of theWhistler mode. In the mirror the wave encounters the resonance conditionω_(o) =2πf_(o) =e B_(RES) /m. Close to said zone the wave-electroninteraction becomes resonant and a large part of the energy of the waveis transferred to the electrons in the form of kinetic energyperpendicular to the force lines of the magnetic field. As a result ofthis energy gain, the accelerated electrons are trapped in the magneticconfiguration, which increases their free average passage and ensures aneffective ionization of the gas in a pressure range which is notaccessible to conventional discharges, where the ionization of the gastakes place by the application of a static electric field.

Another advantage of using the Whistler mode is the avoiding of thelimitation of the electron density of the plasma ne, due to the spacecharge by the condition:

    ω.sub.o =2πf.sub.o <ωpe=|e.sup.2 ne/ε.sub.o m|.sup.1/2

For example at a frequency of 2.45 GHz, a power density of 10 to 20w/cm² makes it possible to obtain with an argon gas at a pressure of 2to 5.10⁻⁴ mbar a density close to 10¹² p/cm³, i.e. approximately 10times the density fixed by the cutoff condition ω_(o) =ω_(p).

For a higher power, the increase in the density leads to a markeddecrease in the phase velocity of the wave in the direction of themagnetic field and the wave propagates perpendicular to the magneticlines in the form of the lower hybrid mode. For such operatingconditions the density of the plasma is fixed by the dispersion relationof the lower hybrid mode defined hereinafter: ##EQU2## in which ω_(pe),i are the electron and ion plasma angular frequencies, ω_(ce) theelectron cyclotron angular frequency, m the mass of the electron and theion, k the wave number and k_(//) its component along the magneticfield. For the example considered hereinbefore at a frequency of 2.45GHz, a power density of 100 to 200 W/cm² makes it possible to obtaindensities of approximately 10¹³ p/cm³, which are not accessible indischarges for the same working pressures.

As the electromagnetic energy is located within the waveguides and atthe working pressures of the source, the movement of the particles beinglinked with the magnetic lines, the dimensions of the plasma generatedby each guide are essentially determined by the dimensions of saidguide. The contiguous association of guides makes it possible togenerate a wave plane perpendicular to the magnetic field over theentire surface of the guides, obtain the resonance condition 2πf_(o)=eB_(RES) /m over the entire width of said surface and produce a plasmalayer, whose dimensions are fixed by the number of associated guides orthe number of guides supplied, as will be explained hereinafter.

These guides can be associated or joined by their large side a in theform of rows and columns, as shown in FIG. 5. This principle is used forcoupling the power in the sources shown in FIGS. 1b/1c and 2b/2c.

These guides can be associated or joined by their small side b, as shownin FIG. 6. The couplers of the sources shown in FIGS. 7a to 7c, 8a to 8cand 9 use this principle.

This method of associating guides makes it possible to adapt the surfaceof the plasma layer generated in the source to the dimensions of theparts to be treated and in particular to the case of large parts. Forexample, at a frequency of 2.45 GHz, an association by the large side ofN=24 standard guides (a=8.6 cm, b=4.3 cm) generates a plasma layer ofheight 8.6 cm and length 100 cm, whilst the association of N=12 of saidsame guides along the small side generates a layer of the same lengthand of height 4.3 cm.

The procedure used for uniformly distributing the microwave powerbetween the guides of the coupler is dependent on the applicationadopted. This power is proportional to the width of the layer andtherefore to the dimensions of the parts to be treated. This power cane.g. be supplied by:

an array of identical, low power emitters P_(VHF) ≈1 KW of the magnetrontype, each magnetron supplying via an adapter and tight window one guideof the coupler;

by an array of identical, medium power emitters P_(VHF) ≈5 KW of themagnetron type, each magnetron supplying several guides of the couplergrouped into identical VHF modules, via an adapter, a planar division Eand a tight window;

a high power emitter P_(VHF) ≈50 KW of klystron type and an equaldistribution of said power between the guides of the coupler byconventional division methods by 3 db coupler or branch guide couplersand automatic adaptation.

A preferred embodiment of the source consists of using a coupler withguides associated or joined along their small side according to FIGS. 7ato 7c, 8a to 8c and 9, said solution permitting:

the reduction of the volume to be magnetized and therefore the volume ofthe permanent magnets and coils and the price of the source,

reducing the microwave power to be used,

facilitating the implementation of the coupler by reducing the number ofguides to be associated for treating a given part width,

facilitating the uniform distribution of the microwave power between theguides of the coupler by supplying each of said guides with amagnetron-type emitter via an adapter or supplying several guides of thecoupler grouped into identical VHF modules via a taper E and H followedby a mode converter adapted to the number of guides of the module.

FIGS. 1a to 1c and 2a to 2c show a conventional example of the use ofsuch sources for coating parts by target sputtering. The neutral gas(Ag,Xe, etc.) introduced into the vacuum enclosure is ionized by thewave and forms a plasma layer, whose dimensions are fixed by those ofthe coupler. In this plasma the electron and ion particles followmagnetic lines and intercept the target over a width fixed by theexpansion or opening out of the force lines and over the entire lengthof the plasma target. The target (Ti, Cr, etc) is electrically insulatedfrom the enclosure. The application of a negative voltage relative tothe plasma leads to a bombardment of the target by the ions of theplasma and the emission of a flux of atoms, which are deposited on thepart to be treated.

Compared with the magnetron method currently used for this coatingprocess, this type of source offers numerous advantages. The ionizationof the gas, the sputtering of the target, the recombination of thetarget atoms on the part to be treated are very strongly decoupled,which gives a very considerable flexibility in the performance of theprocess. The ion density n_(i) in the source is fixed by the gas flowrate .left brkt-top.o and the microwave power P_(VHF) and the velocityof the ions V_(i) bombarding the target by the voltage of the targetV_(c). The deposition rate on the part which is proportional to the ionflux on the target, can thus be controlled independently by means ofthree parameters .left brkt-top.o, P_(VHF) and V_(c). This e.g. makes itpossible to optimize the sputtering coefficient of the ions on thetarget by the target voltage V_(c) and optimize the density in thesource n_(i) with the parameters .left brkt-top.o and P_(VHF). Moreover,in such sources the neutral atoms emitted by the target recombine on thepart to be treated in an area not facing the plasma. Therefore, for aconstant ion flux supplied by the source, the pressure in the work framecan be lowered by using a differential pumping. The mechanism ofionizing by the wave used permits, for a given ion flux on the target,to operate with lower pressures in the source, which limits the densityof the occluded gases in the deposit. The material balance is improvedbecause the entire surface of the target is bombarded by the plasmalayer. Moreover, the target can be changed without dismantling thesource or passing in front of the ion beam for carrying out a continuousprocess.

The wave/particle energy transfer fixing the properties of the plasmatakes place through the electrons. Thus, these sources operate with allgases, gas mixtures and reactive gases.

To obtain high quality metal deposits, the contamination by impuritiescan be reduced by using a coupler made at least partly from the materialof the target employed.

Moreover, in such sources, the plasma density varies linearly with theVHF power density and can approach 10¹⁴ p/cm³ for a power density ofapproximately 1 KW/cm² at a frequency of 2.45 GHz, which corresponds toan ion flux close to 10²⁰ /cm² /s. For such high flux operatingconditions, the target, the enclosure, and the coupler must be cooled.In the proposed solution, each of these elements can be cooled by asimple, known procedure of using a double wall with a flow of coolingfluid in the interior, which is controlled in an independent manner andthe VHF windows are protected against the bombardment of the plasma.

In this source operating mode, the density performances of the plasmalayer can be used for generating electron or ion beams. FIG. 2dillustrates a use of said source for producing electron or ion beams. Inthis case the target is eliminated and replaced by two extractionelectrodes, which make it possible as a function of the polarization toextract the ions or the electrons in the form of a linear beam 17, whoselength is fixed by that of the coupler.

Another embodiment is represented by cusp-type linear microwave sources.The basic diagram of such a source type used for depositing metal layerson substrates is illustrated in FIGS. 13a to 13c and 14a to 14c. FIGS.13a to 13c correspond to the case where the magnetic configuration isproduced by coils. FIGS. 14a to 14c correspond to the case where it isproduced by permanent magnets.

In these drawings, the elements which are identical to those of FIGS. 1ato 1c and 2a to 2c are given the same references.

Such a source uses, as the aforementioned magnetic mirror source, thesame wave-based gas ionization mechanism, the same coupling system byassociated guides making it possible to obtain a wave planeperpendicular to the magnetic field and the resonance condition 2πf_(o)=B_(RES) /m over the entire plasma layer width.

The special nature of this source type is based on the fact that thecurrents flowing through the coils B₁ and B₂ (FIG. 13b) or themagnetization vector in the magnet blocks A₁ and A₂ (FIG. 14b) haveopposite signs, which makes it possible to generate a cusp-type linearmagnetic configuration. This configuration is characterized by a zerofield line on the axis of symmetry of the configuration, a module of thefield B_(x) ² +B_(y) ² =B² which increases at all points around saidaxis, four maxima of the field to the right of the coils or magnets, twoon the axis Ox, B_(xMAX), two in the median plane of the sourceB_(yMAX). The coils and magnets are dimensioned so as to satisfy thecondition

    B.sub.xMAX, B.sub.yMAX >B.sub.RES =2πf.sub.o m/e

over the entire plasma layer width.

Within this condition, the cusp characteristics can vary by acting onthe currents in the coils, the distance between the coils or themagnets, by adding metal parts, arranged in the known manner, so as tomodify the magnetic field lines.

In this configuration, the magnetic field lines from the wave guides ofthe coupler intercept the two targets 2 placed in the enclosure and aresubject to the bombardment of the plasma (FIGS. 7b and 8b). Thesetargets are electrically insulated. The application of a positivepotential leads to an ion bombardment of said targets and the emissionof a neutral atom flux. On penetrating the plasma, these neutral atomsare ionized by high energy electrons created by the wave and form aplasma of metal ions having the composition of the target. By followingthe field lines, these ions recombine on the substrate placed at the endof the cusp in order to form a metal deposit, whose width is fixed bythe opening out of the magnetic lines and the length by that of thecoupler.

Apart from the possibility of producing deposits on large substrates, byits very operating principle this type of source has, compared withother sources which are generally used several significant advantages,namely the ionization mechanism using the wave eliminates pollution ofthe deposit linked with the use of the emissive cathode and permits anoperation of the source at low voltage, which limits the density of theoccluded gases and the cusp-type magnetic configuration adds a newpossibility of checking the nature and quality of the deposit.

The latter point is an important element with regards to the flexibilityof use of such sources. The plasma ensuring the bombardment of thetargets 2 and the emission of the atom flux is generated by theionization by the wave of a carrier gas or metal vapour introduced intothe enclosure. The properties of the deposit on the substrate are fixedby the relative concentrations of the different ion species in theplasma and the relative densities of the excited or neutral atoms andfree radicals. These concentrations can be controlled by independentsettings:

of the ion flux bombarding the targets and which is dependent on theposition, the bias voltage and the temperature of the target, or by thedensity of the magnetic lines intercepted by the target;

the composition, flow rate of the carrier gas or gases and theirinjection point into the source.

For example, for carbon deposits, the carbon concentration can becontrolled by the ion flux on graphite targets, by the choice of thecarrier gas in hydrocarbon form (methane, propane, etc.) carbon oxides(CO, CO², etc.) and the localized independent injection of hydrogen oroxygen.

These sources also operate with refractory material targets, such asoxides of uranium, aluminium, as well as boron and its compounds. Inthis case, the checking or control of the magnetic configuration makesit possible to vary the density of the magnetic lines intercepted by thetargets and therefore the energy density deposited by the plasma and theflow of neutral atoms reemitted by the target. The control of this flow,the flow rate and the nature of the carrier gas (nitrogen, oxygen, etc.)makes it possible to modify the properties of the deposit, as in thecase of metal targets.

The absence of an emissive cathode enables the sources to be operatedwith reactive gases under permanent operating conditions with aremarkable reliability and service life.

Another embodiment is represented by hybrid configuration, linearmicrowave sources. Such a source, like the cusp or magnetic mirrorsources described hereinbefore, uses the same mechanism of ionizing thegas by the wave and the same system of coupling the microwave power withthe plasma.

The special nature of this source type is the magnetic configuration.This so-called hybrid configuration shown in FIG. 15 is generated bysuperimposing a magnetic field with mirror B_(y) (x) created by the twocoils B₁ and B₂ surrounding the vacuum enclosure and a transversemagnetic field B_(x) (y) produced by the two permanent magnet blocks A₁and A₂ arranged on either side of the vacuum enclosure.

The special property of this configuration is that the location of thepoints in the plane xOy, where the module of the magnetic field |B|² =B_(x) ² +B_(y) ² !^(1/2) is equal to the resonant magnetic field|B|=B_(RES) =2πf_(o) m/e is a closed curve C contained within the vacuumenclosure. As the fields B_(x) and B_(y) in the volume of the enclosureare independent of the longitudinal direction Oz, the resonancecondition |B|=B_(RES) is satisfied on the same closed curve C in all theplanes xOy of the vacuum enclosure and therefore on the entire surfaceobtained by the translation of said curve in the direction Oz.

The existence of this closed resonance surface makes it possible toobtain in such a source a plasma with a very high energy electronpopulation which, by successive ionizations, removes the neutral atomsfrom the gas or metal vapour introduced into the enclosure. The ions,charged one or more times as a function of the value of the pressure ofthe gas in the source and which are generated in this magneticconfiguration, are extracted from the vacuum enclosure by extractionelectrodes located at the end of the mirror in the form of a linearbeam, whose length is fixed by that of the coupler.

The properties of the closed resonance surfaces have been successfullyused for the production of circular, multicharged ion beams in magneticconfigurations with a symmetry of revolution.

As a result of the use of a linear magnetic configuration and thegeneration of a layer-type plasma by associating guides according totheir large or small side, the present invention generalizes the conceptof closed resonance surfaces with symmetry of revolution to linearsurfaces and makes it possible to obtain linear ion beams of very largedimensions with high current densities.

The field of application of such sources covers all the conventionalapplications of ion sources, such as ion implantation, deposition withion assistance, etc.

The advantage of this type of source is that it makes it possible toperform these processes on an industrial scale as a result of thedimensions and performance characteristics of the beam of generatedions.

We claim:
 1. Apparatus for the treatment of a surface with the aid of aparticle flux, obtained from the bombardment of a target by a plasmajet, which has a linear microwave source, comprising:an enclosure havinga first plane of symmetry, extending along a length and a width thereof;means (B₁, B₂ ; A₁, A₂) for producing a magnetic field in the enclosureand for generating a plasma layer (P) having a prescribed width andextending along a second plane of symmetry parallel to said first planeof symmetry; coupling means between the microwave emission means and theplasma layer in the enclosure; at least one target (2) comprising atleast one element to be deposited, which is electrically insulated fromthe enclosure and raised to a bias voltage (V_(c)) relative to theplasma layer (P); pumping means (3) for producing a vacuum in theenclosure (1); gas injection means (9) for checking the ion species ofthe plasma layer (P), characterized in that: the magnetic field has aplane of symmetry coinciding with that of the plasma layer (P) and thatof the enclosure (1); and the magnetic field is constant in thedirection of the width of the plasma layer, thereby capable ofestablishing the resonance condition 2πf_(o) =eB_(RES) /m over theentire plasma layer width.
 2. Apparatus according to claim 1,characterized in that the source assembly is grounded.
 3. Apparatusaccording to claim 1, characterized in that the enclosure (1) isparallelepipedic.
 4. Apparatus according to claim 1, characterized inthat the means for producing a magnetic field comprise coils (B₁,B₂)surrounding the enclosure (1).
 5. Apparatus according to claim 4,characterized in that the length of the coils (B₁,B₂) exceeds the lengthof the enclosure (1) so as to eliminate the edge effects linked with thereturn of the current.
 6. Apparatus according to claim 1, characterizedin that the means for producing a magnetic field comprise permanentmagnet blocks (A₁,A₂) positioned on either side of the enclosure (1). 7.Apparatus according to claim 6, characterized in that the permanentmagnet blocks (A₁,A₂) are extended beyond the enclosure (1) in order toprevent edge effects.
 8. Apparatus according to claim 1, characterizedin that the coupling means comprise identical wave guides associatedalong their large or small side in order to generate a wave planeperpendicular to the magnetic field and distribute the microwave poweruniformly over the plasma layer width.
 9. Apparatus according to claim1, characterized in that the frequency of the electromagnetic fieldproduced within the enclosure is in the range 1 to 10 GHz.
 10. Apparatusaccording to claim 8, characterized in that the wave guides are at leastpartly made from the same material as the target.
 11. Apparatusaccording to claim 1, characterized in that it has a mirror-type, planarmagnetic configuration comprising two coil arrays (B₁,B₂) of anidentical nature traversed by identical currents (I₁,I₂) flowing in thesame direction, or two identical magnet blocks (A₁,A₂) hollowed out intheir central portion and placed on either side of the enclosure (1),the magnetic field having two maxima B_(MAX) and one minimum B_(MIN)located between said maxima, the condition B_(MAX) >B_(RES) >B_(MIN)being satisfied over the entire plasma layer width, B_(RES) being thevalue of the magnetic field for which the cyclotron angular frequency ofthe electron is equal to the angular frequency of the electromagneticwave used for producing the plasma.
 12. Apparatus according to claim 1,characterized in that it has a cusp-type, planar magnetic configurationin which the currents (I₁,I₂) flowing through the coil (B₁,B₂) or themagnetization vector in the magnet blocks (A₁,A₂) have opposite signs,the coils and the magnets being dimensioned so as to satisfy thecondition B_(xMAX), B_(yMAX) >B_(RES) over the entire plasma layerwidth.
 13. Apparatus according to claim 1, characterized in that it hasa hybrid magnetic configuration generated by superimposing a mirrormagnetic field produced by the two coils (B₁,B₂) surrounding theenclosure (1) and a transverse magnetic field produced by two permanentmagnet blocks (A₁,A₂) on either side of the enclosure (1).
 14. Apparatusaccording to claim 1, characterized in that the magnetic configurationgenerates in the plasma a planar surface where the resonance condition|B|=B_(RES) is satisfied at all points of said surface.
 15. Apparatusaccording to claim 11, characterized in that it is used for producing asurface coating by sputtering.
 16. Apparatus according to claim 12,characterized in that it is used for producing a deposit of thin metalfilms.
 17. Apparatus according to claim 13, characterized in that it isused for producing ion assistance and implantation.
 18. Apparatusaccording to claim 13, characterized in that the magnetic configurationgenerates in the plasma a planar surface where the resonance condition|B|=B_(RES) is satisfied at all points of said surface.
 19. Apparatusaccording to claim 14, characterized in that it is used for producingion assistance and implantation.